1. Field of the Invention
The invention relates to crosslinkable compositions based on organosilicon compounds which have controllable modulus, to a process for their preparation and to their use.
2. Background Art
Single-component sealants which are storable under the exclusion of water and can be vulcanized to elastomers at room temperature on ingress of water are known. These products are used in large amounts, for example, in the construction industry. Such sealants are based on polymers which are terminated by silyl groups bearing reactive substituents such as OH groups or hydrolyzable groups such as alkoxy groups. It is possible, by virtue of the chain length of the polymers, to influence essential properties of these RTV1 mixtures. The modulus in particular, i.e. the stress value at 100% elongation of a cured test specimen, can be regulated by virtue of the chain length. For jointing sealants, for example, it is desired that the modulus is low, so that only minimum forces can act on the joint flanks. However, for economic and technical reasons, only a restricted range of polymer chain lengths is available for the production of sealant mixtures. Especially the long chain lengths required for very low-modulus sealants lead to very high viscosities of the polymers, so that such products can only be handled with difficulty. A further disadvantage of polymers having high viscosities is that the compositions produced therefrom can only be expelled from the containers with difficulty, since the sealant mixtures also exhibit high viscosity. In addition, it has been known for some time that the amount of unreactive plasticizers and active fillers can be used to vary the modulus. Here, though, since the compositions otherwise, for example in the case of too much plasticizer or too little active filler, become too nonviscous, which results in poor performance of the pasty sealant.
Furthermore, the use of polymers which contain a nonreactive group at some chain ends is known. For example, EP 1 141 132 A1 describes polymers which are obtained by reacting vinyl-terminated polydimethylsiloxanes with Si—H— containing crosslinkers, the crosslinkers being used in deficiency, so that unreactive vinyl groups remain in the polymer mixture. The vinyl-terminated polymers are, however, comparatively expensive, which makes the composition uneconomic for use in sealants. In addition, the preparation of the polymer cannot be integrated directly into sealant production, so that a separate step is needed. EP 916 702 A1 describes polymers which have some trimethylsilyl groups as unreactive end groups in the polymer. In this case too, the polymer has to be prepared separately before the actual sealant production.